This invention relates to amplifiers suitable for operation with signal sources in which the signal to be amplified is in the form of pulses having low signal levels in the presence of switching transient signals of short duration and large level.
Solid state line scanners have been used in applications such as optical character recognition and optical recognition in which generally the level of illumination detected by the line scanner is relatively large. When the line scanner is utilized in a portable radiation measuring system such as disclosed in copending application, Ser. No. 197,453, filed Oct. 16, 1980, MICROPROCESSOR DIRECTED OPTICAL PYROMETER, by Alexander H. Clark, John E. O'Neil, and Albert S. Tenney III, the levels of illumination vary widely. In order to expand the span of the measurement, the solid state line scanner is driven by an adjustable frequency clock. When the level of illumination is low, the frequency at which the line scanner is operated is reduced so that a distinguishable signal may be obtained from the line scanner.
In order to reduce the effect of switching transients in the output signal, line scanners manufactured by EG&G Reticon and identified as their G Series Solid State Line Scanners, incorporate photodiodes and dummy diodes. The purpose of the dummy diode is so that switching transients can be eliminated by connecting an amplifier to be differentially responsive to signals generated by the photodiodes and the dummy diodes. As an alternative approach to eliminating the problem of the switching transient noise, it has been proposed that the output from the line scanner be appplied to an integrating circuit coupled to a sample and hold amplifier to reduce the effect of the switching transient noise.